Peterborough’s expansion from a medieval market town into a major urban centre has left a complex geological legacy beneath its streets. The city sits on the edge of the Fens, where Oxford Clay is overlain by river gravels, alluvium, and extensive areas of made ground from the brickmaking era. This layered stratigraphy means hydraulic conductivity can vary by orders of magnitude within a single building plot. When we run a field permeability test here, we are not simply following a procedure, we are reading the ground’s response to understand how water moves through these contrasting deposits. A test pit investigation often reveals the first signs of this variability, showing lenses of sand within the clay that can act as preferential drainage paths and completely alter the dewatering strategy for a basement excavation.
A single Lugeon test in fissured Oxford Clay often reveals more about the ground's drainage behaviour than a dozen lab permeability tests on intact samples.
Our approach and scope
Site-specific factors
A few years back, a contractor in the Hampton area called us after their sump-and-pump dewatering system failed repeatedly during a deep excavation. They had assumed uniform low permeability based on a desk study that mapped the site as Oxford Clay, but the borehole logs showed a metre-thick band of sandy gravel at 4.5 m depth that was acting as a drain from the nearby Serpentine Lake. Our Lugeon tests in the underlying clay confirmed it was tight, but the Lefranc test in that gravel lens gave a k value of 3x10^-3 m/s, high enough to overwhelm three pumps. The underestimate of inflow nearly caused a base heave failure. That knowledge is a reminder that in Peterborough, where the drift geology is so erratic, a field permeability test at the right depth is not a box-ticking exercise, it is the difference between a dry dig and a flooded excavation.
Watch how it works
Regulatory framework
BS 5930:2015+A1:2020 – Code of practice for ground investigations, BS EN 1997-2:2007 (Eurocode 7) – Ground investigation and testing, BS EN ISO 22282-2:2012 – Geotechnical investigation and testing – Geohydraulic testing – Water permeability tests in a borehole using open systems, BS EN ISO 22282-3:2012 – Geotechnical investigation and testing – Geohydraulic testing – Water pressure tests in rock, BS EN ISO 14688-1:2018 – Identification and classification of soil
Linked services
Lefranc variable head test
The standard method for soils of moderate to high permeability, such as the river gravels found across the Nene valley. We measure the rate of water level recovery after a sudden change in head, calculating k directly from the time-drawdown curve using the Hvorslev shape factor appropriate for the borehole geometry.
Lugeon packer test
Applied in rock or stiff fissured clay where the mass permeability governs drainage. A test section is isolated with inflatable packers and water is injected at stepped pressures. The Lugeon value (1 Lu = 1 litre/minute/metre at 1 MPa) provides a direct measure of rock mass hydraulic conductivity and joint connectivity.
Falling/constant head in standpipe
A simplified field method for preliminary assessments in cohesive soils where a standpipe piezometer is already installed. We use this to establish an initial indication of bulk permeability before committing to a full Lefranc or Lugeon programme, particularly useful on brownfield sites with unknown fill composition.
Typical parameters
Q&A
What is the difference between a Lefranc test and a Lugeon test?
The Lefranc test is designed for soils and measures hydraulic conductivity in an open borehole section, typically using a falling or constant head method. It suits granular deposits like the river terrace gravels common in Peterborough. The Lugeon test is a packer test for rock or stiff, fissured soils; water is injected under pressure into an isolated section of the borehole, and the result is expressed in Lugeon units, reflecting the rock mass permeability including joint and fracture flow.
At what depths should field permeability tests be carried out on a Peterborough site?
The test depths are dictated by the ground model, not a fixed rule. In our knowledge across the city, we typically target the base of any granular layer (gravels, sands), the interface between drift and solid geology (e.g., gravel over Oxford Clay), and within the clay if it appears fissured. For a basement excavation, we test at formation level and at least one intermediate depth. For a deep sewer or attenuation tank, we test the full depth of the proposed excavation.
How much does a field permeability test cost in Peterborough?
The cost for a field permeability testing programme in Peterborough typically ranges from £440 to £800 per test, depending on whether a Lefranc or Lugeon setup is required, the depth of the test section, and the number of tests conducted in a single borehole. A site investigation with multiple tests and a factual report will be at the higher end. We always offer a fixed price after reviewing the borehole logs and agreeing on the test depths.
Why can't I just use lab permeability tests on core samples?
Lab tests on small intact specimens (e.g., in a triaxial cell) measure the matrix permeability of the soil or rock, but they miss the macro-scale features that control drainage in the field: fissures in Oxford Clay, open joints in Cornbrash limestone, or lenses of sand within a clay matrix. A field permeability test captures the mass hydraulic conductivity, which is the parameter you actually need for dewatering design. In fissured materials, the field value can be 100 to 1000 times higher than the lab value.
How long does a Lefranc or Lugeon test take on site?
A single Lefranc test in granular soil typically takes 1 to 2 hours, including setup, saturation, and the falling-head phase. A Lugeon test in rock takes longer because we run a stepped-pressure sequence with at least five pressure stages; expect 2 to 3 hours per test interval. The overall programme duration depends on how many tests are required and the depth of the borehole, but for a typical Peterborough commercial development investigation we plan for one full day of in-situ testing.